There are a number of known devices designed to filter blood. The vast majority of these devices are designed for permanent placement in veins, in order to trap emboli destined for the lungs. For example, Kimmell, Jr., U.S. Pat. No. 3,952,747 (this and all other references cited herein are expressly incorporated by reference as if fully set forth in their entirety herein), discloses the so-called Kimray-Greenfield filter. This is a permanent filter typically placed in the vena cava comprising a plurality of convergent legs in a generally conical array, which are joined at their convergent ends to an apical hub. Each leg has a bent hook at its end to impale the internal walls of the vena cava.
Cottenceau et al., U.S. Pat. No. 5,375,612, discloses a blood filter intended for implantation in a blood vessel, typically in the vena cava. This device comprises a zigzagged thread wound on itself and a central strainer section to retain blood clots. This strainer section comprises a meshed net and may be made from a biologically absorbable material. This device is also provided with attachment means which penetrate into the wall of the vessel.
Gunther et al., U.S. Pat. No. 5,329,942, discloses a method for filtering blood in the venous system wherein a filter is positioned within a blood vessel beyond the distal end of a catheter by a positioning means guided through the catheter. The positioning means is locked to the catheter, and the catheter is anchored to the patient. The filter takes the form of a basket and is comprised of a plurality of thin resilient wires. This filter can be repositioned within the vessel to avoid endothelialization within the vessel wall.
Similarly, Lefebvre, French Patent No. 2,567,405, discloses a blood filter for implantation by an endovenous route into the vena cava. The filter is present in the form of a cone, and the filtering means may consist of a flexible metallic grid, or a flexible synthetic or plastic grid, or a weave of synthetic filaments, or a non-degradable or possibly biodegradable textile cloth. In order to hold the filter within the vein, this device includes flexible rods which are sharpened so that they may easily penetrate into the inner wall of the vena cava.
There are various problems associated with permanent filters. For example, when a filter remains in contact with the inner wall of the vena cava for a substantial period of time, endothelialization takes place and the filter will subsequently become attached to the vena cava. This endothelialization may cause further occlusion of the vessel, thereby contributing to the problem the filter was intended to solve. Except for the Gunther device, these prior art filters do not address this problem.
A temporary venous filter device is disclosed in Bajaj, U.S. Pat. No. 5,053,008. This device treats emboli in the pulmonary artery which, despite its name, is in fact a vein. The Bajaj device is an intracardiac catheter for temporary placement in the pulmonary trunk of a patient predisposed to pulmonary embolism because of hip surgery, stroke or cerebral hemorrhage, major trauma, major abdominal or pelvic surgery, neurosurgery, neoplasm, sepsis, cardiorespiratory failure or immobilization.
The Bajaj device includes an umbrella made from meshwork which traps venous emboli before they reach the lungs. This device can also lyse emboli with a thrombolytic agent such as tissue plasminogen activator (TPA), destroy emboli with high velocity ultrasound energy, and remove emboli by vacuum suction through the lumen of the catheter. This very complex device is designed for venous filtration and is difficult to justify when good alternative treatments exist.
There are very few intravascular devices designed for arterial use. A filter that functions not only in veins, but also in arteries must address additional concerns because of the hemodynamic differences between arteries and veins. Arteries are much more flexible and elastic than veins and, in the arteries, blood flow is pulsatile with large pressure variations between systolic and diastolic flow. These pressure variations cause the artery walls to expand and contract. Blood flow rates in the arteries vary from about 1 to about 5 L/min.
Ginsburg, U.S. Pat. No. 4,873,978, discloses an arterial device. This device includes a catheter that has a strainer device at its distal end. This device is normally used in conjunction with non-surgical angioplastic treatment. This device is inserted into the vessel downstream from the treatment site and, after the treatment, the strainer is collapsed around the entrapped emboli, and the strainer and emboli are removed from the body. The Ginsburg device could not withstand flow rates of 5 L/min. It is designed for only small arteries and therefore could not capture emboli destined for all parts of the body. For example, it would not catch emboli going to the brain.
Ing. Walter Hengst GmbH & Co, German Patent DE 34 17 738, discloses another filter which may be used in the arteries of persons with a risk of embolism. This filter has an inherent tension which converts the filter from the collapsed to the unfolded state, or it can be unfolded by means of a folding linkage system. This folding linkage system comprises a plurality of folding arms spaced in parallel rows along the longitudinal axis of the conical filter (roughly similar to branches on a tree). The folding arms may be provided with small barbs at their projecting ends intended to penetrate the wall of the blood vessel to improve the hold of the filter within the vessel.
Moreover, da Silva, Brazil Patent Application No. PI9301980A, discusses an arterial filter for use during certain heart operations where the left chamber of the heart is opened. The filter in this case is used to collect certain particles not removed on cleaning the surgical site.
What is needed is a simple, safe blood filter for temporary use. For example, a temporary arterial device for use during surgery that neither complicates nor lengthens the surgical procedure would be desirable. Existing prior art devices are inadequate for this purpose.